In IMT-2000 (International Mobile Telecommunication-2000) CDMA communication system, the infection on digital signals by the wireless channel mainly appears as two aspects: one is the noise and interference of the channel; the other is the multipath effect of the channel. The noise is encountered is any communication systems, but as the characteristic of the mobile communication condition, the interference infection is larger than the noise infection while cofrequency interference is the main factor which limits the system performance. There are far and near effect and a plurality of access case especially in the IMT-2000 CDMA system. There may be a plurality of interference user even in a same district. Further, as the complexity of the wireless condition, a signal transmitted by the wireless channel often arrives at the receiving end along many different paths. As there will be different delay when the signal passes different paths, if the delay difference is larger, span interference could be produced.
Generally, the design of the receiver considers to suppress the interference. As for in the ideal Gaussian White Noise condition, the match filter de-expander could be used. In case that there is multipath interference, the Rake multipath diversity de-expand receiver is often used, which needs to estimate for the multipath delay and extent. In case that there is narrowband interference, the common method is to add an adaptive prediction filter before the match filter to estimate narrowband and realize separate with the wideband frequency spreading. In the IMT-2000 CDMA system where there is a plurality of access interference, a plurality of users detection receiver had been highly regarded, which is consisted of a set of match filters and a plurality of users detector. The most typical is decorrelation a plurality of users detector, which has linear complication and best far and near effect suppress capability. The disadvantage is that it needs pseudo code, timing and phase information of all interference users.
The suppress to all kinds of interference by above methods can each be used separately. But in fact, two case often appear: which interference condition is not known and the interference parameter is not known; many kinds of interference are present at the same time. At this point, the receiver which can suppress a certain interference cannot work normally when encountering the channel conditions where another interference or many kinds of interference are present at the same time. There is another method which combines the narrowband interference trapper, the Rake receiver and the decorrelation a plurality of users detector. The disadvantage is that the receiver is very complex even that it can not be realized.
Smart antenna used presently could update the weight value in terms of a certain rule, according to the change of the signal space distribution characteristic. The extent and phase of the weight value could be updated freely. When the update algorithm constricts, this method could maximize the signal interference-noise ratio by using the space characteristic of the expected user signal and the interference signal fully. As Chinese patent No. 03115415, which name is “a beam forming method applied for using in wideband CDMA system” put forward this kind of scheme, the steps of the method comprising: perform airspace process for array signals, including, weight value estimate, beam forming, match filtering in the time domain, including de-interference and de-diffusion and channel estimate, compensation; the invention could perform re-diffusion adding interference iterating, forming reference signal, so that the system structure is simplified and technical difficulty and operand are greatly reduced. But the method cannot achieve optimal in any communication condition.
Chinese patent No. 03114286 which name is “a software defined radio frequency transceiver” published a system structure of new wireless mobile communication system, i.e. Software Defined Radio (SDR) technique and supporting SDR technique have design methods of many functional radio frequency transceivers in the base station of the wireless mobile communication system. The multifunctional radio frequency transceiver is consisted of element parts of several programmable, configurable wideband wireless radio frequency receivers, several wideband wireless radio frequency transmitters, local oscillator signal generator and several intermediate frequency digital signal processors. In the control of the software programming, by loading software of different wireless communication standards to the radio frequency transceiver, the different radio frequency signal, the intermediate frequency signal and the clock signal are generated, the different work frequency range, carrier frequency bandwidth and duplex mode are set, so that the corresponding carrier frequency is processed and the corresponding, different signal processing algorithm are ran. Although the patent incorporated the SDR into the smart antennal technique, it is not illuminated that how to perform the application of different algorithm according to the communication condition.
Although the best system performance could be achieved by using the wireless communication system of adaptive antenna array, but presently in practice, the application still have to solve some critical technique problems. Among other things, the calculating complication and robustness of the adaptive beam forming algorithm is one of the problems which limit the development of the adaptive antennas. Many adaptive beam forming algorithm appeared presently have personal characteristic and applying condition. The algorithm performance is highly affected by the application condition. It is very hard to find an adaptive beam forming algorithm which could have good antiinterference performance while could converge rapidly in any conditions and the calculating complexity is low.
Therefore, the influence to signals by the wireless channel is mainly manifested by that the span interference could be generated by the interference signal, the multipath signal and the multipath signal of larger delay.